1. Field of the Invention
The present invention relates to compressors used in air-conditioners, and more particularly, to variable displacement compressors that employ swash plates to vary their displacement.
2. Description of the Related Art
A variable displacement compressor is a compressor provided with a structure that enables its displacement to be varied. A swash plate compressor is one type of variable displacement compressor. A typical swash plate compressor includes a drive shaft, a swash plate, and pistons. The swash plate (including a structure that couples the swash plate to a lug plate) is mounted on the drive shaft and supported so as to rotate integrally with the shaft. The pistons are accommodated in cylinder bores and coupled to the swash plate. The rotation of the swash plate is converted to linear reciprocation of the pistons. The reciprocation of the pistons compresses fluid that is drawn into the cylinder bores. The inclination of the swash plate with respect to the drive shaft changes the reciprocating stroke of the pistons and thus varies the compressor displacement.
Japanese Unexamined Patent Publication 62-87678 describes one type of swash plate compressor. In this compressor, the structure connecting the swash plate to the drive shaft is simplified. As shown in FIG. 8, a swash plate 60 has a boss 60a. The wall of a hole 62 extending through the boss 60a includes a rounded surface 62a. The swash plate 60 is installed on the drive shaft 61 by inserting the shaft 61 through the hole 62. The radial position of the swash plate 60 is restricted by the sectional contact between the wall of the hole 62 and the drive shaft 61. The rounded surface 62a in the wall of the hole 62 allows the swash plate 60 to incline. This compressor is characterized by the hole 62, which substitutes for sliders and pins that were used in the prior art to incline the swash plate 60 within a predetermined range. The contact between the rounded surface 62a of the hole 62 and the drive shaft 61 guides the inclining of the swash plate 60 and restricts the inclination within the predetermined range. Pistons 63 are coupled to the swash plate 60 and are reciprocated in associated cylinder bores 64. The reciprocation of each piston 63 compresses fluid that is drawn into each associated bore 64.
In the compressor described in the above publication, the compression reaction of the pistons produces a moment that acts on the swash plate 60. A hinge mechanism 67 constituted by an elongated hole 65 and a pin 66 is provided to carry the moment together with the rounded surface 62a, which contacts the drive shaft 61. However, as the inclination of the swash plate 60 is altered, the contact point between the rounded surface 62a and the drive shaft 61 is axially displaced within a predetermined range. The displacement defines a line of contact between the rounded surface 62a and the drive shaft 61. The stress applied between the rounded surface 62a and the drive shaft 61 along the line of contact is relatively great. In addition, the range of the line of contact is relatively long and the contact at each point is repeated limitlessly. This causes wear between the rounded surface 62a and the drive shaft 61. The wear may hinder the precise and smooth inclining of the swash plate 60.